The present invention relates generally to pipettes, and more particularly to a pipette assembly having a suction device and a small volume disposable tip having a capacity with a range of 0.1 xcexcl to 2.0 xcexcl, the disposable tip being removably secured to the suction device.
In molecular biology, and in other fields, pipette assemblies having small volume disposable pipette tips are used. These pipette assemblies basically consist of two parts, one part being a pipette body or suction device (similar to a syringe) and the other being the disposable pipette tip. With the suction device an exact amount of vacuum is produced. The disposable pipette tip is tightly attached to the suction device, and the vacuum produced by the suction device sucks a predetermined volume of liquid into the second part. Such tips are shown in EP 0 743 095 A1, as well as numerous other patents. One commercially available pipette assembly is the Gilson Pipetman(copyright) P-2 model which is provided with a disposable tip having an advertised range of 0.1-2.0 xcexcl. According to their advertisement, there is minimal air space between the piston in the suction device and the sample which makes the results less technique-dependant. However, with the P-2 model, there is an advertised mean error of xc2x112% at 0.2 xcexcl. It is believed that the mean error is due in part to the construction of the disposable tip which is a female part that telescopes over a male part of the suction device. The disposable tip is injected molded and, because it has to go outside the male part, it is rather wide and has a large volume, usually more that 30 xcexcl.
It is an object of the present invention to provide a pipette assembly employing a disposable tip which may be used with very small samples in the range of 0.1-2.0 xcexcl with a high degree of accuracy.
It is a further object of the present invention to provide such a pipette assembly wherein the disposable tips are of low cost.
In summary, the pipette assembly of this invention includes a suction device provided with a female tip receiver, which receives a disposable male tip in the form of a short piece of extruded tubing. The tubing has a very small i.d., for example 0.3 mm. It is preferably formed of Teflon(copyright), or another hydrophobic material. This arrangement has three advantages:
1) The volume of air in the tip can be very small (circa 3 xcexcl) which makes it easier to exactly determine the volume of liquid that is sucked into the tip. The larger the air volume the greater is the risk that the vacuum will thin the air whereby the volume of sample liquid will be reduced. This is of particular importance if the liquid has a high viscosity.
2) The disposable tip, i.e., the short piece of extruded tubing, is extremely inexpensive. The volume of plastic used for the tip is very small and although a new tip is used for each sample the volume of plastic consumed is reduced.
3) The material of the tip can be Teflon(copyright) or another hydrophobic material. This reduces the risk that any of the sample liquid will remain in the tip after extrusion of the sample.
This invention has application in the apparatus shown in U.S. Pat. No. 4,970,892.
The forgoing objects and other objects and advantages of this invention will be apparent to one skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which preferred forms of the invention are illustrated.